Typical electroencephalogram (EEG) electrodes are interfaced to EEG recorders discretely through single-conductor connectors. Multi-conductor connectors can be utilized to connect a plurality of electrodes attached to a patient to a recorder. Combined with the recorder's high input impedance (greater than 100 M Ohms, typically), typical electrode-connector arrangements make EEG signals highly susceptible to induced electrical noise.
EEG recorders take advantage of the fact that EEG signals are measured differentially (e.g., recording the difference between a reference and target channel), to improve the signal-to-noise ratio (SNR) of the useful signal by rejecting the common-mode portion. To the extent that induced noise affects both channels, it is rejected.
However, signal path differences between channels, noise distribution, and the relative position of the source of noise, among other factors, contribute to a portion of induced noise affecting each channel independently. These independent differences can be incorrectly treated by a recorder as legitimate EEG signals. EEG recording quality therefore depends on the relative magnitude of the differential EEG and induced noise signals, among other factors, that directly impact the review and patient diagnosis.